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Soil organic matter content

This is basically just a trimmed down version of the method in the Kellogg Soil Survey Laboratory Methods Manual, Soil Survey Investigations Report No. 42 Version 5.0, pages 495-497. Some details from the SFU Soil Science Lab are also used.

Authorship

Chantal Koechli, Sam Barnett and Nick Youngblut (2015)

Printing this protocol

See Printing protocols in the README

Application

The mineral content consists of the plant ash and soil particles that remain after removal of organic matter. The determination of organic matter by loss on ignition is a taxonomic criterion for organic soil materials (Soil Survey Staff, 2014).

Method overview

Preparation

  • Dry sample overnight at 110oC.
  • Place samples in clean and dry crucibles.
    • Weigh empty crucible weight
    • This is your crucible weight (g)
    • Record which sample is in which crucible.
  • Weigh the sample + crucible.
    • This the the pre-ignition weight (g)

Loss on ignition

  • Place sample in a cold muffle furnace and raise the temperature to 400oC.
    • Optimum furnace ramp time is 5oC/min.
  • Heat sample overnight (16 h)
  • Once cooled, place samples in drying oven for >= 30 min
  • Weigh the sample + crucible.
    • This the the post-ignition weight (g)

Post

  • %_organic_matter = (pre-ignition_weight - post-ignition_weight) / (pre-ignition_weight - crucible_weight) * 100
  • %_mineral_content = 100 - %_organic_matter

Interferences

NOTE: The sample must be placed in a cold muffle furnace to prevent rapid combustion and sample splattering

Safety

Use caution when the muffle furnace is hot. Wear protective clothing and goggles. Handle the heated material with tongs.

Equipment

  • Labled ceramic crucibles (make sure they are clean and dry)
  • Oven, 110oC
  • Dessicator (may need more than one)
  • Muffle furnace, 400oC
  • Electronic Balance, 0.01-g sensitivity
  • A lab notebook for recording values

Procedure

  1. Weigh empty crucible and record crucible weight.
  2. Place a 10 to 15 g sample in a crucible.
  3. Record which crucible contains each sample.
  4. Dry sample at 110oC overnight.
  5. Remove sample from oven and cool in a desiccator.
  6. When cool, record pre-ignition weight to nearest 0.01 g.
  7. Place sample in a cold muffle furnace. Turn on furnace and start programmed run (To set program, see section "Muffle furnace program setting").
  8. For muffle furnace in Lehmann Lab:
    1. Press left most button till it reads "Run".
    2. Press second button to left untill screen reads "Stat off".
    3. Press right most button once. Screen should read "Stat on".
    4. If program needs to be stopped, press second button to right once. Screen should read "Stat off".
  9. Furnace should increase tempereature at a rate of 5oC/min. Then hold at 400oC for 16 h.
  10. Once fernace cools to 105oC, remove samples and place in desiccator to cool.
  11. When cool, record post-ignition weight to nearest 0.01 g.

Report

Report mineral content to the nearest whole percent.

Muffle furnace program setting

  1. Press left most button untill screen reads "Prog List".
  2. Press second button to run through parameters. Parameters can be changed by pressing up or down arrow buttons (the two right buttons).
  3. Hb = OFF
  4. Hb U = 0.0
  5. rmPU = min
  6. dwLU = Hour
  7. CYCn = 1
  8. SEGn = 1
  9. type = rmPr
  10. tGt = 400
  11. rate = 5.0
  12. SEGn = 2
  13. type = dwell
  14. dur = 16.0
  15. SEGn = 3
  16. type = Step
  17. tGt = 105
  18. SEGn = 4
  19. type = End
  20. Endt = dwell

Precision and Accuracy

Precision and accuracy data are available from the KSSL upon request.

References

Soil Survey Staff. 2014. Keys to soil taxonomy. 12th ed. USDA-NRCS